PITTSBURGH , Pennsylvania -LRB- CNN -RRB- -- In what appeared to be the most visible demonstration yet of this week 's G-20 summit , four people attached to a massive banner dangled from a Pittsburgh bridge Wednesday to protest the global economic meeting .

Four people attached to a massive banner dangle from a Pittsburgh bridge Wednesday to protest the G-20 summit .

The banner hung from the West End Bridge over the Ohio River and read like a road sign : `` Danger : Climate Destruction Ahead . Reduce CO2 Emissions Now . ''

Greenpeace , the environmental activist group , claimed responsibility for the stunt . On its Web site , the group said it wanted to send a message to G-20 leaders with the nearly 80-by-30-foot sign , calling for more attention to the issue of global climate change .

`` It is also critical that G-20 leaders agree to kick-start economic recovery through clean energy investment , '' said Damon Moglen , Greenpeace USA 's global warming campaign director , in a message posted on the group 's site . `` It is imperative that developed world leaders do not fail again in Pittsburgh . They must put money on the table to support developing countries . ''

Pittsburgh police arrested nine people in connection with the bridge incident , on charges that included possession of instruments of a crime , disorderly conduct , conspiracy and obstruction . A police spokesperson described the bridge demonstration as a `` very , very dangerous situation . ''

Police also stopped a second Greenpeace group with a banner from repelling off another bridge . Police arrested five people in connection with that incident . iReport.com : Are you in Pittsburgh ?

The two-day Group of 20 summit , which is bringing leaders of the world 's industrialized nations to Pittsburgh , begins Thursday .

CNN 's Carol Cratty contributed to this report

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Greenpeace , the environmental activist group , claimed responsibility for the stunt

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Pittsburgh , Pennsylvania , plays host this week to G-20 summit

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Police stopped a second Greenpeace group from rapelling off another bridge